Cavity resonator with variable tuning



April 27, 1965 F. G. MASON CAVITY RESONATOR WITH VARIABLE TUNING Filed Oct. 6, 1961 FIG., 2

il Patented ispiraY 27,

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3,181,093 CAVH'Y RESONATOR Wlll-l VAREABLE TUNING Francis G. Mason, Weston, Conn., assigner to Aladdin Industries, incorporated, Chicago, lll., incorporation of Illinois Filed Got. 6, 1961, Ser. No. 143,343 3 Claims. (Cl. S33-S3) This in 'ention relates to a variable tuner which is especially applicable to equipment for receiving, transmitting, or otherwise handling ultra high-frequency signais.

One object or' the present invention is to provide a new and improved tuner of the type utilizing a resonant cavity for the variable tuning element.

A further object is to provide a new and improved variable cavitytype tuner which is capable of covering an extremely wide range oi frequencies.

Another object is to provide a new and improved tuner of the foregoing character in which the cavity is provided with a center post, and in which the tuning variation is accomplished by moving a sleeve or other electrode along the center post.

A further object is to provide a new and improved tuner of the foregoing character, in which the center post is formed with two overlapping portions, adapted to be spanned in a variable manner by the tuning electrode.

Another object is to provide a newand improved tuner construction which is especially applicable to a tuner adapted to operate with a high degree of precision over a wide frequency range.

Further objects and advantages of the present invention will appear from the following description, taken in connection with accompanying drawings, in which:

FIG. l is an elevational sectional view showing'a tuner to be described as in illustrative embodiment of the present invention, the View being taken generally along the broken line l-l in FIG. 2.

2 is a cross-sectional View, taken generally along the broken line 2 2 in FlG. 1.

PEG. 3 is a fragmentary, greatly enlarged cross-sectional view, taken generally along the line 3-3 in FG. 1.

FlG. 4 is a developed view of the center post employed in the tuner.

As already indicated, FlGS. l and 2 illustrate a tuner Titi which will iind many applications in equipment for receiving, transmitting, or otherwise handling ultra highfrequency signals. Thus, the illustrated tuner may be arranged to cover the frequency range from 3154000 megacycles, or any other suitable frequency range.

The illustrated tuner l@ actually comprises two similar tuner stages or sections 12o and lib which may be employed as the preselector stages of a superheterodyne radio receiver. For the most part, the following description will be directed to the iirst tuner stage 12a. The second tuner stage 12b may be considered to be the same, except as otherwise specifically indicated.

The illustrated tuner section 12a is of the cavity type and thus comprises a conductive metal body 14 which is formed with an internal cavity or chamber lo. The body la may be in the torm or a metal casting 18, having a cover plate 2li secured to one side thereof. In this case, the cavity 16 is rectangular in shape, but any other suitable shape may be utilized. Thus, the cavity 16 is bounded by end walls 22 and 24, side walls 26 and 28, a top wall 3d, and a bottom wall 32. ln this case, thebottom wall 32 is formed by the cover plate 2i). The side wall 26 is in the form of a partition between the cavities of the rst and second tuner sections 12a and i211.

The illustrated cavity tuner section l2rz is of the reentrant type and Vthus is provided with a center post 34 which extends longitudinally in the cavity 16. ln accord- Vbetween the overlapping sections 35 and 3S.

ance with the present invention, the center post E4 takes the form of two overlapping sections or members 36 and 3S which are connected to opposite end walls ot the body le. In this case, the overlapping portions 3o and 33 are connected to the end walls 22 and 24, respectively.

in order that the tuner may be made with a high degree of precision, yet at moderate cost, the two portions 3o and 33 of the center post 34 are preferably formed as thin patterned metal coatings or members on a cylinder or rod dil, which may be made ot a suitable insulating rnaterial, such as steatite, glass, or various other ceramic or plastic materials. The metal coatings or members which make up the center Ipost sections 36 and 33 may be applied to or formed on the insulating member 4@ in the desired patterns by the utilization of wellknown printed circuit techniques.

A gap or band e2 of the insulating material is provided lt will be seen that the center post section 36 extends from a conductive cylindrical member which is connected to the end wall 22. ilarly, the section 3S extends from a conductive cylindrical member which is connected to the end wall 24. The section 36 is disposed on one side portion of the cylindrical insulating member dd, while the section 33 is disposed on the opposite side portion thereof. The section Se projects toward the end wall 24 but is insulated therefrom. Similarly, the section 38 projects toward the end wall 22 but is insulated therefrom.

Input and output connections rnay be made to the cavity sections l-.Za and i215 in any known or suitable manner. Various input and output elements are well known to those skilled in the art. in the illustrated tuner ld, an input connection is made to the initial tuner -section 12a by means of a coupling loop which is connected between an input terminal 5@ and the cover plate 2d of the body le. A connector 52 may be mounted on the plate Ztl for the purpose of connecting the input terminal Sli to a coaxial input cable. lt will be seen that the loop 45 is disposed longitudinally in the cavity fro, at one end thereof, adjacent the end wall 22 and the center post section 36. With this arrangement, the magnetic field in the cavity is strongest in the end portion of the cavity adjacent the loop 4S.

In the illustrated arrangement, energy is coupled between the cavity sections lZa and lZb by means of a slot L'd which is formed in the partition 26, at the end of the cavity adjacent the end wall Z2 and the loop 43. The slot 5d permits magnetic interlinkage between the tuner sections 12a and 12b so that signals will be magnetically coupled therebetween. Y

The output from the second cavity section lZb may be taken by means of a second coupling loop 56 which is similar to the loop d3 but is connected between one side Zlib of the cavity section i217 and an output lead S8. As shown, the output lead 53 extends through a small opening eil in the side wall 25h and is connected to a diode rectifier 62 which serves as the mixer of the superheterodyne radio receiver. The tuner lll also has an oscillator section 64 which, however, forms no part of the present invention and will not be described in detail.

The resonant frequency ol' the illustrated tuner section 12a is varied by moving an electrode 65 along the center post 3d. As shown, the electrode 66 takes the form of a conductive metal sleeve or cylinder which is slidably received around the center post 3d. Outwardly projecting flanges d and itl are formed on the opposite ends of sleeve 66.

An insulating layer or space is providedbetween the slee-ve 66 and the center post 3e so that the sleeve will be oapacitively coupled to the center pos-t sections 36 and 3S. ln the illustrated construction, the insulating layer tal-:es .the form of a thin coating 72 (FIG. 3) of insulating material on the outside of the center post 34; The coating conveniently may be applied to all of the exposed outer surfaces of the portions 36, 3S, 40, 44 and 46. It will be realized that an insulating film might alternatively be applied to the inside of the sleeve 66. The insulating layer may be made of any suitable low-loss plastic material, such as Telion, which has the particular advantage of reducing the friction between the sleeve 66 and the center post.

The movement of the slee-.ve 66 has the effect of varying the capacitance between center post sections 36 and 33. This in turn has the efect of varying the resonant frequency of the cavity ltuner section. As shown in FIG. 1, the sleeve 66 almost completely surrounds both center post sections 36 and 3S. This represents approximately the position of maximum capacitive coupling between the sections 36 and 33. Thus, the position of the sleeve 66, as shown in FIG. 1, represents approximately the low frequency end of the tuning range. It will be understood that the sleeve 66 is capacitively coupled to both center post sections 36 and 38 and thus is the means of establishing increased capacitive coupling between the center post sections.

The sleeve 66 may be moved to the left, as shown in FIG. l, so as .to disengage Vthe sleeve in a progressive manner from the center post section 3S. of the sleeve reduces the capacitance between the cen-ter post sections 36 and 38. In its position of extreme movement to the left, the sleeve 66 is received around the cylindrical conductor 44 so that the capacitive coupling between the center post sections 36 and 33 is at a minimum. This position represents the lextreme high frequency end of the tuning range.

To provide for the desired movement of the sleeve 6 the tuner is provided with a precision lead screw 74 which may be rotated by any suitable drive. A traveling nut 76 is threaded onto the lead scre-w 74 and is prevented from rotating by means of a guide rod 78. It will be seen that the nut 76 is formed with an arm S0 which engages the upper side portion of the guide rod 78. The lower side portion of the rod 78 may be engaged by an anti-friction pad S2 on the outer end of a leaf spring 84 which is mounted on the underside of the nut 76.

The illustrated nut 76 has a downwardly projecting tongueV 86 adapted to operate -a movable carriage 88 oncarriage .88. Thus, the sleeve 66 is insulated from theV carriage 8S. No external electrical connection is made -to the sleeve 66.

In the illustrated construction, the tongue 86. extends into a slot 90 formed in the carriage S8. v A ball 96 may be interposed between one side of the slot 94 and the tongue 36. The other side'of the tongue maybe engaged by a spring-pressed pin 96 mounted in the carriage 88.

As shown to advantage in FIG. 2, one end portion of the illustrated carriage 8S is formed on its underside with a V-shaped groove i60 which is slidable along a stationary V-shaped wayor slide 102. In this way, the carriage isconstrained to slide along a straight line path. The other end of the sleeve 38 is guided by an upwardly facing fiat surface or Way 104 which maybe formed on the'A upper side of the casting 18. The carriage 88 may be `fitted withran anti-friction pad l06, adapted to slideV along the fiat surface 104.

Such movementV The springs 90 of the cavity sections'12cz and 12bhave the keffect of pulling the carriage 38 downwardly against post 34. To provide additional spring pressure between the carriage 33 and the V-shaped way 102, a leaf spring 10S is mounted on the carriage. The outer end of the leaf spring 10S is provided with an anti-friction pad 110 which engages the underside portion of the guide rod 78.

The illustrated drive arrangements eliminates any play or binding effect between-the various movable elements of the drive, so that the sleeve 66 may be translated easily and with a high degree of precision. The illustrated'drive reduces backlash to such an extent that it is virtually negligible. Thus, the tuner may be reset to a desired position with an extremely high degree of precision.

Aspreviously indicated, the movement of the sleeve 66' along the center post 34 changes the amount of capacitance between the center post sections 36 and 38. In this way, the resonant frequency of the tuner cavity section is varied. An extremely wide range of frequencies may be covered. Thus, the range from 315 to 1000 megacycles may be covered with only about '1% inches of sleeve travel.

The illustrated cavity tuner construction is highly efficient electrically. It has been found that unloaded Q values in the range from 700 to 1100 can readily be obtained.

Various modifications, alternative constructions and equivalents may be employed Without departing from the true spirit and scope of the invention as exemplified in the foregoing description and defined in the following claims.

I claim:

1. In a tuner for ultra high-frequencies, the combination comprising a conductive body having a cavity therein, input and output means for coupling signals to and from said cavity, said cavity having first and second oppositek end walls, a cylindrical center post in said cavity and having first and second longitudinal generally parallel diametrically opposite overlapping conductive portions connected to said first and second end walls, said first and second portions being insulated from each other and having a longitudinal gap therebetween, said center post including a cylindrical insulating member for supporting said first and second portions, said first and second portions being formed as conductive cylindrically curved coatings on diametrically opposite portions of said insulating member, said center post having zin-insulating coating thereon, a conductive sleeve received around said center t post and slidable therealongsaid insulating coating being disposed between said sleeveand said first and second por tions and kbeing effective to afford capacitive coupling therebetween, and means for moving said sleeve along said said center post including a cylindrical insulating member for supporting said first and second portions, said first and second Vportions being formed` as conductive cylindrically curved vcoatings on diametrically opposite portions of said insulating member, said center post having an insulating coating thereon, a conductive sleeve received around said center postA and slidable therealong, said insulating coating being disposed between said sleeve and said first and `second portions and being effective to afford capacitive coupling therebetween, and means for moving said sleeve along said center post for varying the capaci- Vtance between said first and second portions, and thereby varying the resonant frequency of said cavity.

3. In a tuner for ultra high-frequencies, the combination comprising a conductive body having a cavity therein, input and output means for coupling signals to and from said cavity, said cavity having irst and second opposite end Walls, a cylindrical center post in said cavity and including a cylindrical insulating member extending between said first and second end walls, said center post including first and second parallel longitudinally extending diametrically opposite overlapping conductive members connected to said first and second end walls and mounted on the outside of said cylindrical insulating member, said rst and second conductive members being cylindrically curved and being insulated from each other with a longitudinal gap therebetween, a conductive sleeve received around said center post and slidable therealong, means affording insulating material between said sleeve and said first and second conductive members of said center post to provide capacitive coupling therebetween, and means for moving said sleeve along said center post for varying the capacitance between said first and second conductive members so as to vary the resonant frequency of said cavity.

References Cited by the Examiner UNITED STATES PATENTS 2,092,708 9/39 Wheeler 334-41 2,744,220 5/56 Matteson 317-249 2,758,268 8/56 Peyssou 317-249 2,797,583 7/57 Leschenski 7410.85 2,826,698 3/58 Mason 334-41 2,834,216 5/58 Thompson 74-10.85 2,871,345 l/59 Napolin 333-83 X 2,890,425 6/59 Regnier S33-83 X 2,906,329 9/59 Frerer et al. 20G-334 2,994,009 7/61 Schmidt et al 333-83 X 3,090,920 5/ 63 Levine 333--83 X HERMAN KARL SAALBACH, Primary Examiner. 

3. IN A TURNER FUR ULTRA HIGH-FREQUENCIES, THE COMBINATION COMPRISING A CONDUCTIVE BODY HAVING A CAVITY THEREIN, INPUT AND OUTPUT MEANS FOR COUPLING SIGNALS TO AND FROM SAID CAVITY, SAID CAVITY HAVING FIRST AND SECOND OPPOSITE END WALLS, A CYLINDRICAL CENTER POST IN SAID CAVITY AND INCLUDING A CYLINDRICAL INSULATING MEMBER EXTENDING BETWEEN SAID FIRST AND SECOND END WALLS, SAID CENTER POST INCLUDING FIRST AND SECOND PARALLEL LONGITUDINALLY EXTENDING DIAMETRICALLY OPPOSITE OVERLAPPING CONDUCTIVE MEMBERS CONNECTED TO SAID FIRST AND SECOND END WALLS AND MOUNTED ON THE OUTSIDE OF SAID CYLINDRICAL INSULATING MEMBER, SAID FIRST AND SECOND CONDUCTIVE MEMBERS BEING CYLINDRICAL CURVED AND BEING INSULATED FROM EACH OTHER WITH A LONGITUDINAL GAP THEREBETWEEEN, A CONDUCTIVE SLEEVE RECEIVED AROUND SAID CENTER POST AND SLIDABLE THEREALONG, MEANS AFFORDING INSULATING MATERIAL BETWEEN SAID SLEEVE AND SAID FIRST AND SECOND CONDUCTIVE MEMBERS OF SAID CENTER POST TO PROVIDE CAPACITIVE COUPLING THEREBTWEEN, AND MEANS FOR MOVING SAID SLEEVE ALONG SAID CENTER POST FOR VARYING THE CAPACITANCE BETWEEN SAID FIRST AND SECOND CONDUCTIVE MEMBERS SO AS TO VARY THE RESONANT FREQUENCY OF SAID CAVITY. 